It is known that process variations within integrated circuit manufacture can cause components not to have a desired absolute value, and can also cause scaling between components on the same integrated circuit to vary from a desired ratio. It is also known to adjust the values of components after fabrication, but before packaging, by trimming techniques such as laser trimming.
Boundaries between different layers of material within an integrated circuit can give rise to reflections within the integrated circuit being trimmed. These reflections can interfere, both constructively and destructively with the light from the trimming laser. This gives rise to the possibility that some parts of the circuit being trimmed may lie at a region of destructive interference, and therefore may not be heated by the amount that is expected. Similarly, regions of the circuit adjacent the component that is being laser trimmed may be heated more than expected if they lie at regions of constructive interference. These interference effects may affect the time required to perform a laser trim, the outcome of the trimming operation, and the degree of potential damage to adjacent structures within the integrated circuit.